1. Field of the Invention
The present invention relates to a power supply device, a scanner power supply device, and an image forming apparatus.
2. Description of the Related Art
With the recent trend of digitalization of information, an image processing apparatus such as a printer and a facsimile for outputting digitalized data and a scanner for digitalizing documents has come to be an indispensable apparatus. Such image processing apparatus often includes an imaging function, an image forming function, a communication function, and the like to serve as a multifunction product usable as a printer, a facsimile, a scanner, and a copier. There are various demands for such image processing apparatus, one of which is saving power. To meet the demand, an image processing apparatus is proposed, for example, in Japanese Patent Application Laid-open No. 2004-88649, in which light emitted from a scanner light source is received by a photovoltaic mechanism used for a solar energy generation or the like to charge a standby power supply.
In the technology disclosed in Japanese Patent Application Laid-open No. 2004-88649, a storage unit such as a capacitor is charged by power generated by a photovoltaic unit that receives light from a scanner light source and is used as a standby power supply when the capacity of the storage unit has reached a predetermined voltage. However, because of the insufficient light converting efficiency of the photovoltaic unit and the shortage of an amount of irradiated light, a high current value as a generated electric current may not be ensured. In this case, it takes an extremely long time to charge the storage unit depending upon the capacity of the storage unit.
On the other hand, when the capacity of the storage unit is lowered, the storage unit can be charged to a predetermined voltage in a short time; however, only a small quantity of charges can be accumulated. Therefore, the storage unit works as a power supply for only a short time, which is not enough in performance as a standby power supply. Such problem occurs not only to the photovoltaic generation by a scanner light source of an image processing apparatus but also to charging of an electric power generating unit capable of outputting only small current.